The sound a sheet of hardcopy media makes as it moves along a hardcopy media transport path can be used to diagnose the condition of the hardcopy media. Quiet or uniform sounds can indicate a normal or problem-free passage of the hardcopy media along the hardcopy media transport path. Loud or non-uniform sounds can indicate a disruption in the passage of the sheet of hardcopy media such as a stoppage due to jamming or tearing or other physical damage of the hardcopy media.
As an example, in commonly assigned U.S. Pat. No. 4,463,607 a hardcopy media transport cylinder with a specialized profile is used to enhance the diagnostic qualities of the hardcopy media transport noise in order to detect hardcopy media wear. However, this specialized hardcopy media transport cylinder is designed to induce stresses into the hardcopy media that interfere with smooth hardcopy media transport at high transport speeds.
Other known methods of detecting jams include using optical or mechanical sensors in order to detect the times of the passage of a sheet of hardcopy media at various locations along the hardcopy media transport path. If the hardcopy media does not arrive at a given location at a given amount of time after the start of transport, a hardcopy media jam is inferred. The problem with this approach is that optical and mechanical sensors are highly localized in physical detection range, requiring the use of several such sensors situated along the hardcopy media transport path.
Commonly assigned U.S. Pat. No. 8,857,815 describes placing a microphone near the beginning of a hardcopy media feed path in order to detect the sound of a hardcopy media jam in progress. The signal from the microphone is processed by counting the number of sound samples above a given threshold within a sampling window of a given width. If the count is sufficiently large a hardcopy media jam is signaled. In this approach, no information is provided about the location of the hardcopy media as it moves along the transport path. Thus, although sound may be used to detect a jam in progress, information regarding the location of the jam that may be provided by optical or mechanical sensors as discussed above is unavailable.
There remains a need for a fast and robust technique to indicate hardcopy media jams along a hardcopy media transport path that uses a single hardcopy media sensor and processes the signals from the hardcopy media sensor simply, and in a way that incorporates the location of the hardcopy media along the hardcopy media transport path.